Certain applications of a liquid filter permit the use of a permanent filter media. However, permanent filter medias require periodic cleaning, as by backwashing, as taught in my U.S. Pat. No. 5,139,670. Where capacity of the filter is relatively large, backwash efficiency must be maximized. Moreover, because an increase in capacity is normally achieved by increasing the area of the filter media, it is extremely important to minimize unit stress on the filter media. When a permanent filter is utilized on a drum filter, assembly of the filter media onto the drum also presents a problem.